ASSOCIATION OF AGE WITH THE THRESHOLD FOR DETECTING ANKLE INVERSION AND EVERSION IN UPRIGHT STANCE

A randomized quadruple staircase method and probit analysis were used to measure the thresholds for sensation of ankle inversion and eversio n by 18 healthy young and 18 healthy old subjects while standing with a foot in a servo-driven cradle. The results of over 3600 trials show that the mean threshold for detecting inversion with a probability of 75% was 0.35 degrees in the older subjects, a value significantly grea ter than the 0.06 degrees threshold found in the younger group. The co rresponding thresholds in eversion were significantly greater in both old (0.52 degrees) and young (0.35 degrees) subjects. Significant; but smaller, age differences were also found in unipedal stance. Few sign ificant sex differences were found. When the velocity of a 0.1 degrees inversion movement was increased from 2 to 200 degrees/s the probabil ity of detecting it rose by only 22.6%. Although significantly increas ed with age, the threshold for sensing rotation in the weight-bearing ankle was measured in tenths of degrees, an order of magnitude better than previously reported (non-weight-bearing) values.